Color television



Aug. 30, 1949. c. Go| D'MARK' COLOR TELEVISION Filed Sept. 7, 1940 5Sheets-Sheet 1 Aug. 3o, 1949. Y P. c. GQuDMARK 2,480,571 y A coLoRTELEVISIN' A Filed sept. 7', 1940 y 's sheets-sheet 2 ATTORNEYS Aug. 30,1949.` P jc.. zaoLDMARKv 2,480,571 v COLOR TELEVISION Filedsept. 7;1940A s sheeisfsheet s ATTORNEYS Patented ug. 30, 1949 UNITED lSTATESPATENT OFFICE Peter C. Goldmark, New York, N. Y., assignor to ColumbiaBroadcasting System, Inc., New York, N. Y., a corporation of New YorkApplication September 7, 1940, Serial N0. 395,840

successively red, green and blue, this sequence beingcyclicallyrepeated. With three primary colors, either double or quadrupleinterlacing may be method of scanning and reproducing an image innatural colors kwhich gives good color rendition and preserves detail inthe image under widely varying color conditions, Without requiring anexcessive transmission band and without objectionable iiicker. Theinvention also contemplates the provision of apparatus for scanningareas in accordance with the method of the invention.

It has heretofore been suggested to. achieve color television bytransmitting successively images correspondingto theprimary colors inthe object transmitted. The three-color system,

employing red, green and blue iilters, is usuallyemployed. Inthissystemeach transmitted image represents the whole of the object scene asviewed through the corresponding niter, as distinguished from aninterlaced scansion. The system is therefore open to the usual objectionof excessive flicker, unlessthe images are transmitted at a high speed.The required high rate of transmission, since the images are complete,requires an excessive transmission band if detail is to be preserved. Toreduce iiicker, it has also been proposed to simultaneously transmit thered, green and blue images over separate channels, but such a system isundesirably complex.

A system for the interlaced scansion of images in color has also beensuggested, but in this system each set of lines always represents thesaine color in the object eld. With such a system, if the object neldhappened to be all red, for example, or predominantly red, only the redset of lines would be transmitted, the other set or sets ofvlines beingnegligible. Thus a considerable amount of detail would be lost.

In accordance with the present invention, image areas are scanned in aplurality of interlaced iield scansions, successive iield scansionscorresponding to dierent primary colors. However, within a completecycle, each set of interlaced lines represents each of the primarycolors. With this system, if the color of the object field ispredominantly one of the primary colors, that color will be successivelytransmitted by different sets of interlaced lines so that no detail willbe lost. To accomplish this result, the sets of interlaced lines and thenumber of primary colors are made non-multiples of each other, and boththe sets of lines and the primary colors alternate in regular sequence.For example, if three primary colors are employed, eldI scansions areemployed, or in general, any number of sets of lines which is anon-multiple of the number of primary colors. The several interlacedsets of lines are also scanned in regular cyclically recurring sequence.

By employing the system of the invention, excellent color rendition andadequate detail can be\ obtained within the present standard televisionband for black and white pictures without objectionable icker'.hereinafter described the theoretical resolution of the color images issomewhat less than that of black and white images, for the same bandwidth. However, it is found that the eiect on the eye of the addition ofcolor satisfactorily compensates for the theoretical loss of resolution.

The invention will be more readily understood by reference to thedrawings and to the following detailed description thereof.

In the drawings:

Fig. 1 represents schematically a double-interlaced scanning pattern;

Fig. 2 represents a scanning sequence suitable for use in adouble-interlaced, three-color system;

Fig. 3 represents schematically'a quardupleinterlaced scanning pattern;

Fig. 4 represents a scanning sequence suitable for use with athree-color, quadruple-'interlaced system;

Fig. 5 illustrates diagrammatically a television color-nlm transmitteremploying a continuously moving nlm, adapted for use with the scanningsequence of Fig. 2;

Figs. 6, '7 and 8 are detail views of elements ofthe scanning apparatusof Fig. 5;

Fig. 9 is a diagram illustrating the scanning of a film-frame duringsuccessive scansion periods;

Fig. 10 illustrates diagrammatically a colornlm transmitter employing anintermittently moving nlm;

Fig. 11 illustrates a scanning sequence for the apparatus of Fig. 10when transmitting in accordance with the system of Fig. 2; and

Fig. 12 illustrates diagrammatically a color television receiver adaptedfor use with the systems of the invention.

. Fig. 1 illustrates a conventional double-interlaced scanning patterncomposed of one set of lines a, and a second set of lines b interlacedwith the a lines. The pattern is scanned in the usual manner, one set oilines, say thea lines, being In some specic embodiments scanned from topto bottom in a so-called fieldscansion period. The b lines a thenscanned during the next neid-scansion period. The frequency with whichthe scanning point returns to the starting corner is referred to as the"ield frequency" and the transversal of the iield as one eld scansion.regardless of whether every second. fourth, etc. line is traced at eachtraversal. The frequency with which every line of the eld is scanned isreferred to as the e frequency or image frame frequency. this beingone-half, one-quarter, etc., of the field frequency, depending onwhether double, quadruple, etc., interlacing is used. Y

Referring to Fig. 2, a scanning System is illustrated for use with adouble-interlaced, threecolor system. The sawtooth wave represents thelow-frequency or vertical scanning wave. Alternate scanning waves aremarked a and the intervening scanning waves marked b, indicating therespective set of lines being scanned during that field scansion period.Below each wave is indicated, by way of example. the respective colorbeing scanned at that time.` The letters R. G and B are used to denotered, green and blue, these being selected as representative of athree-color system. Of course, other primary colors may he employed, ifdesired, in accordance with well known principles of color reproduction.It will be noted that the interlaced sets of lines cyclically recur inregular sequence, and that the colors cyclically recur in regularsequence. However. the first red image is formed by the a lines, and thesecond red image formed by the b lines. Similarly` esch of the othercolors is composed successively of a and b lines. After six scansionperiods, each color has been reproduced by each set of lines, whereuponthe cycle begins again.

For convenience, suitable legend has been placed on Fig. 2. The term"image ileld is applied to a single scansion of one set of interlacedlines. 'I'he term image frame is applied to' two iield scansion periodsdining which both seis of lines are scanned, although they are scannedin different colors. The term color icld is applied to the period duringwhich each color is reproduced once, or the period between succemivescansions of the same color, this being equal to three field scansionperiods. The term "color frame is applied to the period within whicheach color is reproduced by each set of lines.

At the present time the standards for black and white transmission callfor the reproduction of pictures by double-interlaced scansion, with aiield frequency of 60 iield scansions per second. This gives a framefrequency of 30 frames per second. In the present system, in order toimprove color rendition without iiicker, it is proposed to increase theileld frequency to. say, 120 field scansion per second, thus making theimage field period $520 second. This gives an image frame period of $60second, a color iield period of 1/40 second, and a color frame period of1150 second, as indicated in Fig. 2. These specific values are of coursegiven for purposes of illustration only. If the eld period were changed,the other periods would be changed accordingly.

With the speciiic values given in Fig. 2, all three colors arereproduced within 40 second, each color being reproduced by one set oflines. Assuming the most disadvantageous case in whichtheimageisailoneprimarycolor,sayred,aredimagewillbereproducedbyeithertheaorb lines at intervals of 340second, and a complete redimageformedbybothsetsoflineswillbe reproducedwithin lo second. Thus serious difiiculties due to flicker are avoided.Also, no detail is lost since both set of lines are reproduced in thiscolor. Of course, in most instances at least small amounts of the otherprimary colors will be present so as to assist in reducing flicker.

Auming a transmission band width just sufiicient to reproduce the fulldetail of 441 lines per frame for black and white pictures, inaccordance with present standards, the equivalent resolution of thesystem of Fig. 2 will be 44h/72me lines per frame. Although theresolution for color is somewhat lower due to the fact that the iieldfrequency has been increased, the addition oi color compensates for thetheoretically lower denition and yields a very satisfactory image. Ofcourse, a wider band would permit greater deiinition.

Figs. 3 and 4 illustrate a quadruple-interlaced system. Such a system,although somewhat more complicated than the double-interlaced system ofFig. 2, has the advantage that it provides higher deiinition for thesame band Width. Fig. 3 illustrates the conventional system ofquadruple-interlaced scansion. Lines a are iirst scanned from upper leftto lower right, then the lines b halfway between the lines a are scannedfrom upper left to lower right, then lines c and lines d. Of course, thepresent invention is not limited to the scansion of the four sets oflines in the particular order given.

Fig. 4 illustrates a scanning sequence in which successive saw-toothwaves correspond to successive sets of lines. The image field period isassumed, for example, to be M30 second. Successive sets of linescorrespond to successive colors, yielding a vcolor field period of V60second as shown. The image frame, during which each set of lines isscanned once, is Q5 second. A complete color frame, during which eachcolor is reproduced by all of the four sets of lines, is 5&5 second.Even if the image were all red, the fact that component red images recurat V30 second intervals reduces dicker, and the fact that the red imageis reproduced by all four sets of lines yields full definition.

Assuming again a band width just suicient to reproduce 441 lines perframe at a double-interlaced eld frequency of 60 deld scanslons persecond, as ilxed by present standards, the equivaient denition for thecolor system of Fig. 4 would be 441V=360 lines per frame. Thisrepresents an increase in definition over that of Fig. 2 for the sameband width. As in the case of Fig. 2, further definition could beobtained by a broader band.

In Fig. 4, in parentheses, are given the periods for an assumed iieldscansion period of 1/120 second. The color iield is 1/m second, theimage geld 1/ao second, and the color 'frame 1/10 second. With suchvalues, full 441 line definition could be obtained with presentstandards. To reduce interline flicker, the scanning lines could beincreased to 550, for example.

It will be noticed that in both Figs. 2 and 4, the number of colors,namely three, is not a multiple of the number of sets of lines. whichare two and four, respectively. Also, the number of sets of lines is nota multiple of the number of colors. This non-multiple relationshipyields the advantageous result that each color is repro- 'I5 ducedsuccessively by a diderent set of lines. Ii

a diderent number or ors or a diile'rent num-v ber oi sets oi lines wereemployed, this non-multiple relationship could be preserved and theadvantagesof the present invention retained.

Fig. illustrates a nlm scanner' suitable for use with the systems of'the invention.v The apparatus is particularly ldesigned lor use withstandard motion picture sound nlm requiring an average rate ofreproduction of 24 iilm frames per second, and for use with the scanningsystem of Fig. 2. A film IB, threaded over sprockets Il, is driven withcontinuous uniform movement by motor I2 at the required rate of 24 ilhnframes per second. The nlm is of the color type, for example, of theTechnicolor or Kodachrome type. The lm gate I3 is illuminated with lightfrom a suitable projection source such as the arc 'Il and condenser lensI5. Other sources of light could of course be employed. The illm gate islonger than that of a single iilm frame in order to permit each filmframe to be scanned a plurality of times during its travel through thegate. In the specific embodiment described, the iilm gate is designed toexpose an area of the same width and 8/5 the height of a lm frame.

The system for projecting images from the iilm to the cathode I6 of thescanning tube I'I, here shown as a tube of the Farnsworth ImageDissector type, is a modification of that shown in Figs. 13 and 14 of mycopending application Serial No. 210,607, filed May 28, 1938, for Methodand apparatus for television," now Patent No. 2.287.033. As theredescribed, the projection lens I8 is positioned to form an enlargedvirtual image of the iilm in a plane behind the iilm, such as plane i9.Small lenses I, 2, 3, 4 and 5 operatesuccessively to project virtualimages in the plane I9 to the cathode I6 of the image dissector. Thesmall lenses I-5 are rendered successively operative by the shutter disk2l driven by motor I2. The shutter disk is illustrated in Fig. 6, andconsists of an opaque disk having slots I', 2', 3', t' and 5' cuttherein. As the disk rotates, these slots successively uncover the smalllenses.

In the path of light from the lm is positioned a color disk 22. Thisdisk is illustrated as located between the plane of the lm and theprojection lens i8. However, it might also be placed on the oppositeside of the rllm or at any convenient location between the plane of theillm and the cathode I6 of the image dissector. The disk should bedesigned and located so that the cathode I6 is illuminated with light ofsuccessive primary colors during successive eld scansions. Whenpositioned as shown, the disk may be constructed as shown in Fig. 7.'I'he disk should be large enough so that each lter segment R. G, Bsuccessively covers the lm gate, and large enough so that the transferfrom one color sector to the next takes 'place during a blanking period.If desired. the

lter segments may be constructed in the manner described in my copendingapplication Serial No. 355,839, :tiled concurrently herewith, now PatentNo. 2,304,081. An infrared lter is placed in 'amsn s ouslyTheheatdiskisillustrafedin It willbe that with a scanning device of thenon-storage type it is necessary to illuminate a line of the film onlyat the time that particular line is being scanned. The heat disktherefore contains slots I", 2", 3", 4" and 5", extending through equalcentral angles, one for each o! the small .projection lenses I 5. Forthe speciilc case illustrated, slots I" and 5" are continuations of eachother. For a dierent specinc.

embodiment, this might not be true. The width oi the slots is such as toexpose only a fraction of a film frame to light from the projectionsource at any one time. In the limiting case this might be one line, butto avoid diiliculties due to curvature of the slots and the necessity ofmaintaining very accurate phase relationships, the slots are preferablymade wide enough to cover a number o! scanning lines at a time. Theconstruction of the slots will be explained more fully hereinafter,after consideration has been given to the manner in which the iilm isscanned.

Referring to Fig. 9, two adjacent iilm frames 25 and 26 are illustratedin the positions which they occupy in the lm gate during five successiveheld-scansion periods I, II, III, IV and V of film frame 25, and I' oflm frame 26. It will be understood that since the nlm-frame period is21; second and the ield-scansion period 1/120 second, iive eld scansionswill take place during one nlm-frame period. Also. the lm frame movesdownwardly a distance of VSH, where H is the heighth of a nlm frame,during each iield scansion period.

At the beginning of the rst field-scansion period, the villm frame 25 isin the position shown at I. Small lens I is rendered operable by slot I'in the shutter disk and the image of film frame 25 is projected onto thecathode i6 of the image dissector. The electron image in the imagedissector is deflected by suitable means (conventional and therefore notshown) to scan horizontal lines oi the ilm frame at line-scanningfrequency. The electron image is also deflected by suitable means (notshown) in a vertical dlrection to scan the image in a vertical directionat eld-scanning frequency.

Since the nlm is continuously moving downwardly, the vertical deectionof the electron image need be only %H, in order to scan the full heighthof the iilm frame during the scansion period. At the end ofthe first eldscansion the ilm frame 25 has reached the position shown at II.Projection lens 2 is thereupon rendered operable by slot 2' of theshutterdisk and the same illm frame rescanned from bottom to top. Sincedouble interlacing is employed, the eld scansion I will be of one set oflines, say the a lines, and field scansion II will be of the b lines.The required interlacing may be produced in the usual manner. At the endof eld scansion II, the film frame 25 will be in position shown at III.The a lines of the same illm frame will then be rescanned from bottom totop. This procedure is repeated for the remaining field scansion periodsIV and V. 'I'he cycle is then repeated and the next lm frame 26 scannedin similar manner. It will be noted that the b lines of film frame 26will be scanned during the ilrst field scansion period I'. Successivefield scansions will alternate between a lines and b lines. The dottedlines of Fig. 9 indicate diagrammatically the deilection of the scanningbeam.

As explained in my copending application :filter for scansion period In.The colors are then repeated for successive field scansion periods, Rand G being operable for scansion periods IV and V. The blue filter B isoperable during eld scansion I of the next iilm frame 26. It will benoted that for any given nlm frame, two colors are reproduced by bothsets of interlaced lines but the third color by only one set. Theparticular color reproduced in only one set of lines changes forsuccessive hlm-frame periods, and the single color reproductionalternates between a and b lines. Therefore no diiiiculty arises.

Continuing the description of the heat disk of Fig. 8 in conjunctionwith Fig. 9, slot i" is operable during ileld scansion I. The beginningoi the slot exposes the lower lines of the lm frame 25 and as the heatdisk rotates, slot I" progresses toward the top of the lm frame toexpose areas as they are scanned. Since the ilm frame moves downward1/5H during the iield scansion period, the end of the slot need bedisplaced' radially only %H with respect to the beginning thereof. Forscansion period II, slot 2" operates and exposes iilm frame 25 in thesame manner as in the previous scansion period, theslot beginning at thebottom of the lm frame and progressing toward the top as the diskrotates. The beginning and end of slot 2" is displaced lnwardly a radialdistance of H with respect to the beginning and end of slot I", tocompensate for the displacement of the continuously moving illm duringthe rst scansion period. Slots 3", 4" and 5" are positioned in a similarmanner to expose film frame 25 during respective scansion periods III.IV and V. Corresponding points of successive slots will be displacedinwardly a radial distance of MSH to compensate for lm movement. At theend of the iilm frame period, slot I" again comes into operation toexpose the succeeding film frame 26 during field scansion I' of that lmframe, etc.

The shutter disk 2I, the color disk 22, the hea disk 23 and the lm I0are all driven by the same motor I2, in order to preserve propersynchronous relationships. For the speciiic embodiment disclosed, theeld frequency is 120 field scansions per second, the lm is driven at a.rate of 24 illm frames per second, shutter disk 2I rotates at 1440 R. P.M., the color disk 22 at 2400 R. P. M. and the heat disk 23 at 1440 R.P. M. Suitable coupling means are provided between the several disks,the lm drive and the motor to secure these relationships. Also, thedeiiection system (e. g., a saw-tooth wave generator) and the motor aremaintained in synchronous relationship.

As shown in Fig. 9, the lm gate needs to be iii-,H in height, in orderthat each lm frame may be scanned iive times as it passes through theapparatus.

It will be clear that the apparatus of Fig. 5, as described, operates toscan the lm in accordance with the scanning system of Fig. 2, and yieldsa video signal of which successive portions represent diierent coloraspects and diierent sets oi lines of an object eld, as will be clearfrom Fig. 2. It should be pointed out that the term image frame" is notsynonymous with nlm frame, nor is the term frame-scanning frequencyidentical with film-frame frequency. Image frame period relates to thescanning of a ileld in both a lines and b lines, and frame-scanningfrequency relates to the frequency of repetition of both a lines and blines. On the other hand, nlm-frame period relates to the period duringwhich a single lm frame is scanned, and lmframe frequency relates to therate at which illm frames pass through the apparatus. The differencewill be clear by consideration of Figs. 2 and 9.

The heat disk 23 may be employed in other types of ilm scanners whereinit is desired to expose only a portion of the lm frame area at any onetime, the particular area exposed progressing as scanning proceeds. Thenumber of slots and shape of the slots may be altered in accordance withthe particular scanning device with which it is used.

Referring to Figs. 10 and 11, apparatus is shown employing anintermittently moving film. Film I0 is drawn through gate I3 by anintermittent film moving mechanism of suitable construction, not shown.In this embodiment the film gate need expose only the area of one lmframe. The film in the gate is illuminated by a suitable projectionsource such as the arc I4 and condenser lenses I5. Images in the lm gateare projected by lens 3| to the mosaic 32 of the scanning device, hereshown as a tube 33 of the storage type. As examples of such tubes, theIconoscope and "Orthicon may be mentioned. Suitable scanning means (notshown) for scanning the mosaic in horizontal and vertical directions arepro vided.

Sincethe scanningv tube is a storage device, it is desirable to projectthe image onto the mosaic 32 only during the blanking period. Thereforea flashing shutter 34 driven by motor 35 is provided. Shutter 34 isopaque, and has openings therein at suitable intervals so that as thedisk rotates, the mosaic is periodically exposed to light from the illmimage. Preferably the openings are of such shape as to expose all partsof the mosaic equally, as is known in the art. A color illter disk 36,which may be of the same type as shown in Fig. '1, is also disposed inthe path of light from the image to the mosaic. If desired, it could ofcourse be placed near the plane of the film on either side thereof asshown in Fig. 5.

Fig. ll illustrates diagrammatically the scanning procedure'. At theleft of the gure, V' represents the last field scansion of a given iilmframe. During the blanking period immediately preceding this scansion,the iield frame is projected through the blue lter B by a light pulse31. The light pulse should be of suiiieient intensity to adequatelyeXDOse the mosaic oi the scanning tube even though the duration of thepulse is very short. The b lines of the lm frame -are scanned duringthis iield scansion. During the scanning, the ilm is moved to the nextiilm frame.

At the end of the iield scansion V', the succeeding film frame isprojected onto the mosaic through the red lter R by a light pulse 38.The a lines of the iilm frame are thereupon scanned during scansionperiod I. During the next blank- -ingperiod the mosaic is exposedmomentarily through the green lter G and the b lines scanned f duringfield scansion II. scansion proceeds during periods III, IV and V in themanner indicated in Fig. 11. During scansion period V the film is movedto the next film frame, and the scanning procedure repeated beginningwith I", except that the b lines are scanned first.

The scanning system of Fig. 4, when an image field period of l/iaosecond is used, is not as conveniently adapted for use with the usualcommercial motion picture sound lm as that of Fig. 2, since the fieldscansion period of l/ 1an second is not as conveniently related to theiilm' frame frequency of 24 frames per second. The system may of coursebe used with specially re-. corded film designed for use with theWstem.v With an image eld period of 1/120 second, the system of Fig. 4may conveniently be used with ordinary sound motion picture film. Boththe systems of Figs. 2 and 4 may be used with direct pickup devices.

Fig. 12 illustrates receiving apparatus suitable I for reproducingimages in color in accordance with the systems described hereinbefore.The cathode-ray reproducing tube 4l, which may be of conventional type.is provided with the usual pair of horizontal deilecting plates 42 andvertical deiiecting plates 43. These are suitable for electrostaticscanning and may, of course, be replaced by corresponding coils forelectromagnetic deflection. The horizontal deflecting plates 42 areenergized by the saw-tooth generator 44 at line-scanning frequency, andthe vertical deflecting plates 43 are energized by generator 45 atnaald-scanning i'reouency. Conventional means may be employed forsecuring double, quadruple or other interlaced scanning patterns inaccordance with the invention. These are known in the art and hence neednot be described in detail. An electron beam generated by the electrongun 45 is deflected by the pairs of plates and scans a field'on the endof the tube. The end of the tube is covered with fluorescent material 41to reproduce visual images.

In front of the tube. and preferably closely adjacent thereto. ispositioned a color filter disk 48. This disk may be of the form shown inFig. '7, and is rotatable about axis 49 by a motor 5|.

. The motor is synchronized with the field scanning. and the drivingratio between the motor and the disk is selected with respect to thenumber of color sectors so that successive interlaced images areexhibited through successive color sectors. That is. the lter sectorstraverse the end of the tube at held-scanning frequency. The disk shouldbe of large enough diameter to vobscure the scanning lines on theuorescent screen at the time they are scanned. Also. it is advantageosto have the lines obscured for a considerable interval after scanning,so that the lines are exhibited through the proper color filter duringthe period of afterglow. The lter disk may advantageously be constructedin the manner described in my copending application, Ser. No. 355,081.filed concurrently herewith, now Patent No. 2,304,081.

For transmitters employing storage tubes, instead of employing anintermittently moving film, a continuous film projector which projects astationary image could be employed.

It will now be appreciated that the present invention provides scanningsystems of general utility for both direct pickup and fllm scanning,

particular apparatus described herein, the apparatus being for purposesof illustration only. Modifications are of course possible which comewithin the spirit and scope of the invention as described and claimedherein.

What I claim is:

1. In color television. the method of scanning a eld which comprisesscanning said field in a plurality of interlaced iield scansions,successive interlaced field scansions corresponding to different colorsof a plurality of primary colors. said plurality of primary colors andsaid plurality of interlaced field scansions being non-multiples of eachother.

2. In color television transmitting and receiving systems, the methodoiscanning which comprises scanning a field in a plurality of cyclicallyrecurring interlaced field scansions, successive eld scansionscorresponding to different colors of a plurality of cyclically recurringprimary colors, said plurality of primary colors and said plurality ofinterlaced field scansions being non-multiples of each other and saidfield scansions recurring at the rate of at least 120 fields per second,whereby each set of interlaced scanning lines cyclically corresponds toeach of said primary colors and objectionable color :dicker may beavoided.

3. In color television transmitting and receiving systems, the method ofscanning which comprises successively scanning a plurality of interlacedsets of lines of a field during respective successive field scansionperiods, successively scanned sets of lines corresponding to differentcolors of a plurality of cyclically recurring primary colors, saidplurality of interlaced sets of lines and said plurality of primarycolors being non-multiples of each other and said field scansionsrecurring at the rate of at least 120 fields per second, whereby eachsetof interlaced scanning lines cyclically corresponds to each of saidprimariar rotors and objectionable color iiicker may be avoided.

4. In color television transmitting and receiving systems, the method ofscanning which comprises cycllcally scanning a field in two interlacedsets of lines at the rate of at least 120 eld scansions per second, saidsets of lines being successively scanned during respective eid scansionvperiods, to form a double interlaced scanning and at receivers. It willbe understood that the transmitting said video signal to a reproducer,

scanning systems are not coniined to use with the pattern, said fieldscansions corresponding successively to three cyclically recurringprimary colors, whereby each primary color cyclically corresponds toeach set of interlaced lines and objectionable color flicker may beavoided. 5. In color television transmitting and receiving systems, themethod of scanning which comprises cyclically scanning aield in fourinterlaced sets of lines at the rate of at least field scansions persecond, said sets of lines being successively scanned during respectiveeld scansion periods to form a quadruple interlaced scanning pattern,said eld scansions corresponding successively to three cyclicallyrecurring primary colors, whereby each primary color cyclicallycorresponds to each set of interlaced lines and objectionable colorflicker may be avoided.

6. In television, the method of transmitting and reproducing images incolor which comprises scanning an object field at the transmitter in aplurality of interlaced field scansions to thereby generate a videosignal, successive interlaced eld scansions corresponding to dierentcolors of a plurality oi' primary colors, said plurality of primarycolors and said plurality of interlaced iield scansions beingnon-multiples of each other,

and reproducing from said video signal by said reproducer successiveinterlaced images corresponding to successive interlaced fieldscansions, successive interlaced images being reproduced in respectivedifferent colors of a plurality or primary colors, said plurality ofinterlaced images and said plurality of primary colors at the reproducerbeing non-multiples of each other.

7. In color television, a transmitting scanning device for scanning animagefield in a plurality of interlaced eld scansions, successiveinterlaced iield scansions corresponding to different colors of aplurality of primary colors, said plurality of primary colors and saidplurality of interlaced field scansions being non-multiples of eachother, means for transmitting signals corresponding to said eldscansions to a receiver, and means at said receiver for reproducing fromsaid signals interlaced eld scansions in colors respectivelycorresponding to said eld scansions,

8. In color television, means for projecting a Vlight image of an objecteld to a transmitting scanning device, means associated with saidscanning device for scanning said object eld in a plurality ofsuccessive interlaced eld scansions at the rate of at least 120 eldscansions per second, means for successively interposing in the path oflight of said scanning device during successive field scansion periods aplurality of different color filters, said plurality of interlaced ieldscansions and said plurality of color lters being non-multiples of eachother, means for transmitting signals corresponding to said fieldscansions to a receiver, a reproducing scanning device at said receiveradapted to reproduce from said signals interlaced eld imagescorresponding to said interlaced field scansions, and means associatedwith said reproducing scanning device ior exhibiting successive iieldimages in colors respectively corresponding to said eld scansions,whereby improved color rendition may be obtained and objectionable colorflicker avoided.

9. In a color television transmitter, the combination which comprisesscanning means for scanning an image field in a plurality of interlacediield scansions at the rate of at least 120 field scansions per second,means associated with said scanning means for successively presentingdiierent color aspects of said image field to the scanning means duringrespective eld scansion periods, the means for presenting differentcolor aspects being correlated with the scanning means so that each ofsaid color aspects is cyclically scanned by different sets of interlacedlines, whereby a signal providing improved color rendition withoutobjectionable color flicker may be obtained.

10. In a color television transmitter, the combination which comprisesscanning means for scanning an image eld in a plurality of interlacediield scansions, means associated with said scanning means forsuccessively presenting a plurality of primary color aspects of saidimage iield to the scanning means during respective iield scanslonperiods. said plurality of primary-colors and said plurality ofinterlaced eld scansions being non-multiples of each other and said eldscansions recurring at the rate of 120 per second or more, whereby eachcolor aspect is cyclically scanned by different sets of interlaced linesto improve color rendition and objectionable color icker is avoided.

11. In a color television transmitter, the cornbination which comprisesa scanning device for scanning an image eld in a plurality of cyclicallyv recurring interlaced lield scansions at the rate of 120 fieldscansions per second or more, means associated with said scanning devicefor successively presenting a plurality of cyclically recurring primarycolor aspects of said image iield to the scanning device duringrespective eld scanslon periods, said plurality of primary colors andsaid plurality of interlaced field scansions being nonmultiples of eachother so that each color aspect is cyclically scanned by dilerent setsof interlaced lines, whereby a signal providing improved color renditionwithout objectionable color iiicker may be obtained.

12. In a color television transmitter, the combination which comprisesscanning means for successively scanning a plurality of interlaced setsof lines of an image iield during respective successive eld scansionperiods, means associated with said scanning means for successivelypresenting a plurality of cyclically recurring primary color aspects ofsaid image field to said scanning means during respective successivelield scansion periods, said plurality of primary colors and saidplurality oi interlaced sets of lines being non-multiples of each otherand said field scansions recurring at the rate of 120 per second ormore, whereby each set ot interlaced scanning lines cyclicallycorresponds to each of said primary colors to improve color renditionand objectionable color iiicker is avoided.

13. In a color television transmitter, the combination which comprises ascanning device for successively scanning a plurality of interlaced setsci' lines of an image iield during respective successive iield scansionperiods, a color lter device interposed in the path of light to saidscan ning device and adapted to expose said scanning device successivelyto diierent colors of a plu- Cil rality of primary colors of said imagefield, saidl plurality of primary colors and said plurality ofinterlaced sets of lines being non-multiples of each other. and meansfor synchronizing said color iilter device and said scanning device toexpose said scanning device to said different colors successively duringrespective successive iield scansion periods, whereby each set ofinterlaced scanning lines cyclically corresponds to each of said primarycolors, said eld scansions recurring at the rate of 120 per second ormore to avoid objectionable color flicker.

14. In a color television transmitter, the combination which' comprisesa scanning device for cyclically scanning an image field in two sets ofinterlaced lines, said sets of lines being successively scanned duringrespective neld scansion periods at the rate of at least 120 eldscansions per second to form a double interlaced scanning pattern, meansamociated with said scanning device for successively presenting to saidscanning 50 device three cyclically recurring primary color aspects ofsaid image field during respective successive iield scansion periods,whereby each primary color is cyclically scanned by each set ofintei-laced lines to improve color rendition and obljectionable colorflicker is avoided.

15. In a color television transmitter, the combination which comprises ascanning device for cyclically scanning an image eld in four sets ofinterlaced lines, said sets of lines being successively scanned duringrespective field scansion periods at the rate of at least 120 i'leldscansionv per second to form a quadruple interlaced scanning pattern,means associated with said scanning dcvice for suocsively presenting tosaid scanning device three cyclically recurring primary color aspects ofsaid image field during respective successive iield scansion periods,whereby each primary color is cyclically scanned by each set ofinterlaced lines to improve color rendition and objectionable colorflicker is avoided.

16. In a color television receiver, the combination which comprisesscanning means for reproducing images in a plurality of successiveinterlaced field scansions at the rate of at least 120 field scansionsper second, means associated with said scanning means for presentingsuccessive field scansions in diiierent primary colors, said means forpresenting different primary colors being correlated with said scanningmeans so that each of said primary colors is successively presented bydifferent sets of lines of the interlaced i'leld scansions, wherebyimproved color rendition may be obtained and objectionable color ickeravoided.

17. In a color television receiver, the combination which comprisesscanning means for reproducing images in a plurality of successiveinterlaced eld scansions, means associated with said scanning means forpresenting field scansions in a plurality of successive primary colorsduring respective iield scansion periods, said plurality of primarycolors and said plurality of interlaced field scansions beingnon-multiples of each other and said field scansion recurring at therate of at least 120 per second, whereby each color cyclicallycorresponds to diil'erent sets of interlaced lines to improve colorrendition and objectionable color icker is avoided.

18. In a color television receiver, the combination which comprises ascanning device for reproducing images in a plurality of successivecyclically recurring interlaced field scansions, means associated withsaid scanning device for presenting field scansions in a plurality ofcyclically recurring primary colors during respective field scansionperiods, said plurality of primary colors and said plurality ofinterlacediield scansions being non-multiples of each other and saidfield scansions recurring at the rate of at least 120 per second,whereby each color cyclically corresponds to different sets ofinterlaced lines to improve color rendition and objectionable colorflicker is avoided.

19. In a color television receiver, the combination which comprises ascanning device for successively reproducing a plurality of interlacedsets of lines of an image during respective successive field scansionperiods recurring at the rate of at least 120 per second, meansassociated with said scanning device for successively presenting saidinterlaced sets of lines in a plurality of cyclically recurring primarycolors during respective successive iield scansion periods, saidplurality of primary colors and said plurality of interlaced sets oflines being non-multiples of each other, whereby each set ofinterlacedlines is-` cyclically presented in each of said lprimarycolors to improve color rendition and objectionable color flicker isavoided. I

20. In a co-lor television receiver, the combination which comprises ascanning device for successively reproducing a plurality of interlacedeach other, and means for synchronizing s aid color filter device andsaid scanning device to present said different colors successivelyduring respective successive vfield scansion periods, said fieldscansion periods recurring at the rate of per second or more, wherebyeach set of interlaced lines is cyclically presented in each of saidprimary colors to improve color rendition and objectionable colorilicker is avoided.

21. In a color television receiver, the combination which comprises ascanning device for reproducing an image in two sets of interlacedlines. said sets of interlaced lines being successively reproducedduring respective successive field scansion periods recurring at therate of 120 per second or more to form a double interlaced image, meansassociated with said scanning device for successively presenting saidsets of interlaced linesv in three cyclically recurring primary colorsduring respective successive field scansion periods, whereby eachprimary color is cyclically presented by each set of interlaced lines toimprove color rendition and objectionable color flicker is avoided.

22. In a color television receiver, the combination which comprises ascanning device for reproducing an image in four sets of interlacedlines, said sets of interlaced lines being successively reproducedduring respective successive eld scansion periods recurring at the rateof 120 per second or more to form a quadruple interlaced image, meansassociated with said scanning device for successively presenting saidsets of interlaced lines in three cyclically recurring primary colorsduring respective successive field scansion periods, whereby eachprimary color is cyclically presented by each set of interlaced lines toimprove color rendition and objectionable,

color flicker is avoided.

23. An interlaced multiple-color television scanning system comprising,means for periodically scanning the image to be transmitted orreconstructed in frames of n interlaced fields, and means forperiodically changing the color of illumination associated withsuccessive fields not greater than m times per ield and in a series of mcolors, the ratios of n to m and of m to n both being non-integral sothat corresponding fields of -successive frames are associated ywithillumination of different colors.

24. In color television, the method of scanning a field which comprisesscanning said ileld in a plurality of interlaced eld scansions,successive interlaced eld scansions corresponding to difterent colors ofa plurality of primary colors, said plurality of primary colors and saidplurality of interlaced field scansions being non-multiples of eachother and said field scansions recurring at the rate of at least 120elds per second to avoidobjectionable color flicker.

25. In television, the method of transmitting and reproducing images in`color which comprises scanning an object field at the transmitter in aplurality of interlaced eld scansions at the rate of at least 120 fieldscansions per second to thereby generate a video signal, successiveinterlaced field scansions corresponding to diilerent colors of aplurality of primary colors, said plurality of primary colors and saidplurality of interlaced field scansions being non-multiples of eachother, transmitting said video signal to a reproducer. and reproducingfrom said video signal by said reproducer successive interlaced imagescorresponding to successive interlaced field scansions,successiveinterlaced images being reproduced in respective diiierentcolors oi a plurality of primary colors, said plurality of interlacedimages and said plurality of primary colors at the reproducer beingnon-multiples of each other, whereby improved color rendition may beobtained and objectionable color flicker avoided.

26. In color television, a transmitting scanning device for scanning animage field in a plurality of interlaced iield scansions at the rate ofat least 120 iield scansions per second, successive interlaced fieldscansions corresponding to diilerent colors of a plurality of primarycolors, said plurality of primary colors and said plurality ofinterlaced eld scansions being non-multiples of each other, means fortransmitting signals corresponding to said eld scansions to a receiver,and means at said receiver for reproducing from said signals interlacedeld scansions in colors respectively corresponding to said fieldscansions, whereby improved color rendition may be obtained andobjectionable color iiicker avoided.

REFERENCES CITED The following references are oi record in the 111e ofthis patent:

` UNITED sTA'ms PATENTS Great Britain Oct. 25, 1938 OTHER REFERENCESFernseh A. G. (Fernseh Atkiengesellschaft, Berlin) 1. Band Beit 5, Aug.1939, Pases 171 to PETER C. GOLDMARK. 25 179,

